1. Field of the Invention
The present invention is in the field of semiconductor manufacturing and pertains more particularly to methods and apparatus for applying an etchant to decapsulate all or a portion of an encapsulated electronic device.
2. Discussion of the State of the Art
Plastic packaging of various electronic devices, including semiconductor chips, is a well-known process that has been practiced for a long time. Typically, an epoxy or other plastic resin is molded around a semiconductor device creating a chip package. The molding protects a central portion of a lead frame and bonding wires or other connections between contact pads on the chip or device to inner lead fingers on the lead frame. It is often required to decapsulate such a semiconductor package at least in part to allow for device inspection, device testing and, if needed, repair of the chip and or wire bonds to the chip and inner lead fingers after the encapsulation material) covering these elements is removed.
Most commonly, concentrated acids such as sulfuric acid and fuming nitric acid and other liquid materials are used in the decapsulation process to etch the resin material. One challenge in decapsulation systems of prior art is controlling the exact amount of etchant injected into the process. Moreover, a related challenge is preventing damage to the package under process, including preventing damage to interior copper or other metal wires or metal components of the device.
It is desired in some cases that devices which are already attached to a printed circuit board (PCB) or other substrate be decapsulated without removing the semiconductor device from the PCB or mounting substrate. Removing the solder may create additional defects. Additional operational artifacts can be confused with defects built into the device or defects resulting from mounting the device to the PCB or substrate.
Prior art decapsulating systems are also limited in the size of device that can be mounted by the size of the etch plate and safety cover. Prior art systems have the etch plate or etch head centrally located. Therefore to accommodate, for example, a six inch square sample, the etch plate and cover must be over 12 inches square, lending to a system that is too large to handle the pressurization on the cover and etch plate. Some systems use an etch plate manufactured of virgin polytetrafluoroethylene (PTFE) and supported only on the periphery of the system. The higher pressure range may damage or deform the etch plate.
Yet a further limitation of prior decapsulating systems is that due to triboelectric characteristics of the PTFE etch plate, high electrostatic discharge from the plate may occur during movement of the device from the plate and fixture. Furthermore, if the device is mounted to a PCB or substrate there is a possibility of electrostatic discharge (ESD) damage to PCB interconnects and the clamping apparatus holding the device cover down.
Therefore, what is clearly needed is a decapsulation system that eliminates the problems described above.